Tissue‐specific oxylipin signature of tomato flowers: allene oxide cyclase is highly expressed in distinct flower organs and vascular bundles

Abstract

A crucial step in the biosynthesis of jasmonic acid (JA) is the formation of its correct stereoisomeric precursor, cis(+)12-oxophytodienoic acid (OPDA). This step is catalysed by allene oxide cyclase (AOC), which has been recently cloned from tomato. In stems, young leaves and young flowers, AOC mRNA accumulates to a low level, contrasting with a high accumulation in flower buds, flower stalks and roots. The high levels of AOC mRNA and AOC protein in distinct flower organs correlate with high AOC activity, and with elevated levels of JA, OPDA and JA isoleucine conjugate. These compounds accumulate in flowers to levels of about 20 nmol g-1 fresh weight, which is two orders of magnitude higher than in leaves. In pistils, the level of OPDA is much higher than that of JA, whereas in flower stalks, the level of JA exceeds that of OPDA. In other flower tissues, the ratios among JA, OPDA and JA isoleucine conjugate differ remarkably, suggesting a tissue-specific oxylipin signature. Immunocytochemical analysis revealed the specific occurrence of the AOC protein in ovules, the transmission tissue of the style and in vascular bundles of receptacles, flower stalks, stems, petioles and roots. Based on the tissue-specific AOC expression and formation of JA, OPDA and JA amino acid conjugates, a possible role for these compounds in flower development is discussed in terms of their effect on sink-source relationships and plant defence reactions. Furthermore, the AOC expression in vascular bundles might play a role in the systemin-mediated wound response of tomato.

Biochemical and Molecular Characterization of a Hydroxyjasmonate Sulfotransferase from Arabidopsis thaliana

“…Furthermore, a distinct ratio of several octadecanoid-derived compounds, the so-called "oxylipin signature" may have a biological significance. For instance, such a signature was found to be different among various plant species (11) and attributed to distinct defense status (12), and varied also in the same species during development (13).…”

Signaling in Plant Resistance Responses: Divergence and Cross-Talk of Defense Pathways

“…"Early genes", i.e., those rapidly induced after wounding, including those encoding prosystemin and some of the JA biosynthetic enzymes, are expressed in vascular bundles (Jacinto et al, 1997;Kubigsteltig et al, 1999;Hause et al, 2000), whereas "late genes", i.e., those for SWRPs with a direct role in plant defense, are expressed in palisade and adjacent spongy mesophyll cells (Shumway et al, 1976;WalkerSimmons and Ryan, 1977;Ryan, 2000). The temporally and spatially separated expression of the two classes of genes led to the suggestion that wound-signaling events may initially be activated in the vascular bundles to produce second messengers (octadecanoids, OGAs, H202) that will then induce defense gene expression in mesophyll cells (Orozco-Cárdenas, 2000;Ryan, 2000).…”

Jasmonate-induced 23kD protein, JIP-23, is involved in seed development of barley

“…Creelman and Mullet (1997) reported that jasmonates are essential for the development of sink tissues during, for example, fruit ripening, the production of viable pollen and root growth. Further, mRNA of allene oxide cyclase (AOC), the key enzyme of Jasmonate biosynthesis, accumulates abundantly in sink tissues notably flower buds, flower stalks and roots (Hause et al 2000); expression was also shown to be induced by glucose. These data suggest that jasmonate biosynthesis may be induced by sugar imported to sink tissues and that newly synthesized jasmonates then may activate development of these tissues.…”